This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Embedded variable rate coding, also referred to as layered coding, generally refers to a speech coding algorithm which produces a bit stream such that a subset of the bit stream can be decoded with good quality. Typically, a core codec operates at a low bit rate and a number of layers are used on top of the core to improve the output quality (including, for example, possibly extending the frequency bandwidth or improving the granularity of the coding). At the decoder, just the part of the bit stream corresponding to the core codec, or additionally parts of or the entire bit stream corresponding to one or more of the layers on top of the core, can be decoded to produce the output signal.
The International Telecommunication Union Telecommunication Standardization Sector (ITU-T) is in the process of developing super-wideband (SWB) and stereo extensions to G.718 (known as EV-VBR) and G.729.1 embedded variable rate speech codecs. The SWB extension, which extends the frequency bandwidth of the EV-VBR codec from 7 kHz to 14 kHz, and the stereo extension to be standardized bridge the gap between speech and audio coding. The G.718 and G.729.1 are examples of core codecs on top of which an extension can be applied.
Channel errors occur in wireless communications networks and packet networks. These errors may cause some of the data segments arriving at the receiver to be corrupted (e.g., contaminated by bit errors), and some of the data segments may be completely lost or erased. For example, in the case of G.718 and G.729.1 codecs, channel errors result in a need to deal with frame erasures. There is a need to provide channel error robustness in the SWB (and stereo) extension, particularly from the G.718 point of view.